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Russ White 6th March 2013 11:09 PM

The Asynchronous USB Audio class 2 module.
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Well Folks,

It has been a long time coming, but it is almost here. I spent many months of prototyping and research before ending up here.

I am just finalizing the layout of the Asynchronous USB 2.0 input module.

I wanted to show you folks a quick preview of the module. We are just about to order the prototypes.

Some features:

Fully asynchronous operation based on XMOS technology utilizing custom firmware.

All audio signals and power including the clocks are fully isolated from the USB side of things - this can be overridden with jumpers if you want to power the entire device from the USB bus. External power for the audio side is very flexible. 5 - 12VDC input should be fine.

I2S (TTL and LVDS for teleporter) and SPDIF output.

Access to the master clock signal.

All digital audio signals (clocks and data) are re-clocked to the audio master clock.

Two extremely low phase noise Crystek clocks for the audio master clocks.

Separate TPS7A47 LDO regulators used on both the USB side and the audio side.

Meticulous 4 layer layout with very careful attention to all of the important details like signal termination and bypass/decoupling. There is even ESD protection for the USB input.

uFL connectors for LVTTL signals to/from DAC/ADC.

The board is designed to be easily panel mounted using brackets.

Here is a preview of the board. Some details will likely change a bit as I finish it up (and if I find anything I want to change after the next prototypes), and certain design features are intentionally obscured. But you should get a good idea what is going on. :cool:

More details to come. Feedback welcome.


barrows 6th March 2013 11:21 PM

Wooo Hooo!
Thanks Russ. This looks to be great. I am very excited that this is not too far off now...

francolargo 6th March 2013 11:23 PM

Excellent! Still 2 channels/board?


Russ White 6th March 2013 11:25 PM


Originally Posted by barrows (
Thanks Russ. This looks to be great. I am very excited that this is not too far off now...

Me too! I am really excited to move it from prototype to production.

I have a prototype - but it's a bit ugly at the moment. :)

Russ White 6th March 2013 11:26 PM

Yes two channels, may do an eight -channel version later. :)

labjr 6th March 2013 11:31 PM


nycavsr2000 6th March 2013 11:37 PM

Yippee! What's it been? 2 years? I see something happening by summer...



Russ White 6th March 2013 11:44 PM

Well in many ways - 2012 was a year I would rather forget - lets just say there was not much time for my hobby.

In any case - this design is pretty radically different from what I was first going to do. In a very good way. :cool:

hochopeper 7th March 2013 12:39 AM

This will do simultaneous i2s input and output, right?


Russ White 7th March 2013 01:37 AM


Originally Posted by hochopeper (
This will do simultaneous i2s input and output, right?


Yes - it is planned to support that - but I need to actually test it with the target DAC and ADC at the same time.

I have it designed to work with the ESS ADC with the ADC in asynchronous slave mode.

With my current firmware the USB module must always be master for both the DAC and the ADC.

The initial focus is output - but I have plans for input too. :)

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